Really cool game with a nice execution! The art was very interesting and unique. I am not sure if I like it, but it is definitely a really cool idea. The gameplay worked really nicely, and the screen zoom when you killed an enemy gave a nice impact and juice to the shots as well! Some music would have been great as well, but I understand :)
I think the main criticism I have is about the camera. The enemies would suddenly appear on screen and you often have very little time to react. I think it would have helped a lot if the camera were to look a bit 'forward', so you can see what comes ahead. The way I always do it is that I dont center the camera on the player, but I center the camera halfway between the player and the mouse position. This way you can move the mouse to look around.
Very nicely made! Great job :D